After completing the first two levels of the game, you should have enough LEGO Pieces access this Easter Egg. Go into the wizard town through the Leaky Cauldron, the last shop on the left (before the bank), sells custom spells. Purchase the spell called 'Multicorfors'(a spell that turns the characters into "gingers"). Cast it on Ron Weasley. Once cast, he will shake his head as if it has worn off, but his hair will not revert back to its natural color.